Currie following stray energy test system

ABSTRACT

The specification discloses a system for monitoring stray energy on a breech cap firing circuit on ejector racks, used in military aircraft weapons release systems to indicate on a GO/NO-GO basis whether the stray energy will prematurely fire the weapons. The system includes a pair of inputs coupled to an indicator by way of a series switch and a filter. The filter is calibrated to follow a predetermined voltage-time response curve which defines the threshold limits at which the stray energy will prematurely fire the release system. If the threshold limit at any point on the curve is reached, the filter produces a predetermined output which is sensed by threshold circuitry to actuate the indicator and turn off the series switch.

United States Patent Williams et al.

CURRIE FOLLOWING STRAY ENERGY TEST SYSTEM Inventors: Robert A. Williams,Fort Worth,

Tex.; David M. Holt, Fremont, Calif.

Williams Instruments, lnc., Fort Worth, Tex.

Filed: Dec. 22, 1971 Appl. No.: 210,794

Assignee:

U.S. Cl. 324/72, 304/133 Int. Cl. G0lr 19/16, GOlr 31/02 Field of Search324/51, 72.5, 72, 324/133; 328/114, 132; 317/49 6/1972 Trim 324/133 X3/1963 Filipowsky 328/114 X 3,624,503 11/1971 Barrowcliff 324/133Primary ExaminerGerard R. Strecker Att0rneyWm. T. Wofford et al.

[57] ABSTRACT The specification discloses a system for monitoring strayenergy on a breech cap firing circuit on ejector racks, used in militaryaircraft weapons release systems to indicate on a GO/NO-GO basis whetherthe stray energy will prematurely fire the weapons. The system includesa pair of inputs coupled to an indicator by way of a series switch and afilter. The filter is calibrated to follow a predetermined voltage-timeresponse curve which defines the threshold limits at which the strayenergy will prematurely fire the release system. If the threshold limitat any point on the curve is reached, the filter produces apredetermined output which is sensed by threshold circuitry to actuatethe indicator and turn off the series switch.

12 Claims, 5 Drawing Figures CURRIE FOLLOWING STRAY ENERGY TEST SYSTEMBACKGROUND OF THE INVENTION This invention relates to an electrical testsystem for testing the energy level across the electrical contacts in abreech cap firing circuit to determine if the level of stray energy at agiven time is greater than the threshold limit at which the firingcircuit will be actuated.

As explained in U.S. Pat. Nos. 3,505,635 and 3,555,490, pyrotechniccartridges are now extensively utilized in aircraft for ejecting bombsor other weapons. These cartridges are releasably connected withelectrical circuitry, which when energized, detonates the cartridge,thus emitting a high-pressure gas which may, for example, release alatching device and immediately thereafter eject a bomb. Such deviceshave proven dangerous during the arming of aircraft prior to theirmissions. Premature ejection of a bomb may occur if the stray energyacross the firing circuit builds up to a certain level within a certainperiod of time. Accordingly, it is essential that the firing circuit ofsuch devices be tested prior to arming the weapons system to determinewhether the stray energy is greater than the threshold level at whichthe firing system will be actuated.

SUMMARY OF THE INVENTION In accordance with the present invention thereis provided a stray energy test system for measuring the stray energy ona breech cap firing circuit employed on weapons release systems. Thetest system comprises a pair of inputs adapted to be coupledelectrically to the contacts of the system to be tested; a filter forfollowing a predetermined voltage-time curve and for producing apredetermined output when the energy applied to the inputs approaches orreaches the voltage limit of the curve for a given time; an indicator;and a threshold device coupled to the output of the filter for actuatingthe indicator when the predetermined output is produced by the filter.

In a further aspect, a switch is coupled between the contacts and thefilter for passing to the filter the energy applied to the inputs.Current flow through the switch is maintained relatively constant whenthe input voltage varies above a certain level thereby maintainingconstant the input impedance to the filter to enable the filter tofollow the voltage-time response curve. In a further aspect means iscoupled between the threshold device and the switch for rendering theswitch nonconductive when the predetermined output is applied to thethreshold device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a housing whichcarries the test system of the present invention and which iselectrically coupled to a test probe;

FIG. 2 illustrates one end of the housing showing test indicators and aswitch;

FIG. 3 is a schematic diagram of the circuitry of the test system of thepresent invention;

FIG. 4 is a voltage-time response curve which the test system of thepresent invention may follow to determine whether the level of strayenergy is at or above the threshold limit at which a firing circuit maybe actuated; and

FIG. 5 illustrates a front end switch employed to switch out the frontend diode bridge of the circuitry of FIG. 3.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1,reference numeral 11 identifies a housing in which the circuitry of thetest system of the present invention is located. Coupled to thecircuitry in the housing 11 is a test probe 13 for insertion into apyrotechnic cartridge well or breech cap. The

test probe may be of the type disclosed in U.S. Pat.

Nos. 3,505,635 or 3,555,490. It contains a pair of contacts forcontacting the electrical contacts of the weapons firing system to betested. The contacts of the probe 13 are coupled to the circuitry in thehousing 11 by way of electrical conductors located in the cableillustrated at 15.

The test circuitry for testing the firing circuit of the weapons systemincludes input terminals; a series switch; a filter for following apredetermined response curve; a visual stray energy test indicator; anda threshold device coupled from the output of the filter to the seriesswitch and to the visual indicator. Also provided is a mechanical switchwhich may be actuated to carry out test or self-test operations.

In FIG. 2, the mechanical switch is illustrated at 17 and is supportedat the back end of the housing 11. It may be moved from the off to theon (test) or self-test positions to carry out test or self-testingoperations. The visual stray energy test indicator is illustrated at 19.It indicates, in the test condition, whether the firing circuitry beingtested is functioning properly or in selftest, whether the circuitry ofthe test system is functioning properly. Self-test is always carried outbefore test. Also supported by the back end face of the housing 11 is ahigh voltage indicator 2] for indicating whether a very high voltageexists across the firing circuit being tested.

Referring to FIG. 3, the input terminals of the test circuitry areillustrated at 23A and 23B. These terminals are coupled to the pair ofcontacts of the test probe by way of conductors in the cable 15. Theseries switch is a transistor illustrated at Q2. The filter coupled tothe switch O2 is illustrated at 25.

The input across the contacts of the firing circuitry being tested isapplied to the series switch Q2 by way of the contact pair of the testprobe 13, the conductors in cable 15, the input terminals 23A and 23B,and by way of diodes CR1, CR2, CR3, and CR4. These diodes rectify theinput signals so that AC or DC or any polarity input voltage may beapplied to the circuit. For any polarity input, the CR3 and CR4 junction(emitter of Q2) is always more negative than the CRl-CR2 junction whichis the common point of the test circuit.

From the series switch Q2, the input being tested is applied to thefilter 25. The output of the filter at 25A is applied to a thresholdsensing circuitry comprising transistors Q6 and Q5 connected in adifferential-pair type circuit. This threshold device controls theseries switch Q2 and the visual indicator 19 as will be describedsubsequently.

The filter 25 has been calibrated to follow a response curve of the typeillustrated in FIG. 4. This curve is a function of voltage and pulsewidth or time. It has been found that for a given firing circuit of arelease system, stray energy on the firing circuit, when it reaches acertain threshold level as a function of time, will cause the firingcircuit to be actuated, thereby prematurely firing the release system.The curve of FIG. 4 was obtained by testing a given firing circuit of arelease system to determine at what energy or voltage levels, as afunction of time, the firing system would be actuated by stray energy onthe circuit. This curve was derived by computing the arithmatic mean ofthe maximum and minimum values obtained from testing operations in whicha firing circuit would be actuated as a function of time.

The filter 25 in its operation integrates the input applied thereto andif the input, as a function of time, corresponds to the threshold limitsof the firing circuit, the filter 25 will produce a given output in thepresent embodiment, a 0.5 volt output in the negative direction withrespect to common. At that point, the filter has matched the responsecurve at a given voltage and time, thereby indicating that the thresholdlimits of the firing circuit has been exceeded and the firing circuitwill prematurely be actuated by the stray energy there across. Thus foreach point along the curve of FIG. 4, the filter will produce a 0.5 voltoutput in the negative direction and hence will follow the curve whichdefines the threshold limits of the stray energy or voltage as afunction of time at which the firing circuit will be actuated.

The output of the filter is sensed by the threshold sensing circuitryincluding transistor Q6. When the output reaches 0.5 volts in thenegative direction, the threshold device will be actuated to immediatelyturn off the series switch Q2 and also to actuate the indicator 19 toindicate that the firing circuit is faulty and should be repaired beforethe weapons system is loaded. By turning off series switch Q2, the testcircuitry is disconnected thereby protecting the circuitry from a highinput voltage.

The filter 25 shown is essentially a two stage filter with resistors R7,R8 and R9 and capacitor C1 providing a low frequency (long pulsedurations) response filter and resistors R7, R9 and R10 and capacitor C2providing a high frequency response filter (short pulse durations) withthe crossover of the two filter stages at approximately 1.0 millisecondpulse durations. In one embodiment, resistors R7, R8, R9 and R10 wererated at 23.7 ohms, 2.21 kiliohms, 8.25 kiliohms, and 301 ohmsrespectively. In addition capacitors Cl and C2 were rated at 0.68 and0.27 microfarads respectively.

The input impedance to the circuitry is maintained at about 25 ohmswithin the range of about 1.5 to volts input. The input impedance seenat the test circuit input is a function of resistor R7 (resistor R9being large enough to be neglected), the voltage drops across the inputdiodes CRl-CR4, the collector-emitter voltage drop of Q2 and the emittercurrent of Q2. The base current of O2 is held relatively constant bytransistor Q1 and resistor R3, whenever the input to the terminals 23Aand 23B is between about 1.5 to 15 volts. Thus no matter what the inputvoltage within this range, the CR1-CR4 voltage drops, or the Q2collector-emitter drop, the input still sees resistor R7 plus a constantamount of current, which is large enough to overshadow changes in diodesCR1-CR4 voltage drops and the Q2 collector-emitter drop. Thus thecircuit appears to have a constant input impedance for voltages fromabout 1.5 to 15 volts thereby enabling the filter to follow the responsecurve within this range.

A more detail description of the circuitry of FIG. 3 and the elementsthereof now will be given. The switch 17 comprises a manually controlledswitch in which ganged switching elements 17A and 178 may be movedsimultaneously to contact the test terminals T, the off terminals 0, orthe self-test terminals S-T respectively.

In one embodiment, the indicator 19 comprises a commercially availablemagnetic latching indicator (bistable) and which comprises a ballsupported for ro tation in a chamber and which has half of its outershell painted black and the other half painted white. An electricalpulse applied to the indicator will rotate the ball to one of its twopositions whereby either its white side or its black side is viewable tothe observer. When the switch 17 is moved to the test position, theindicator will reflect the black side of the ball if the firingcircuitry being tested is satisfactory and does not have stray energyabove the threshold limits at which the firing system will be actuated.This is defined as the GO condition (for the test position of switch 17)and indicates that the weapons system may be safely loaded. If the strayenergy however is above the threshold limits, then the indicator 19 willreflect the white side of the rotatable ball. This is defined as theNO-GO condition (for the test position of switch 17) and indicates thatthe firing circuit is faulty and must be repaired before the weaponssystem is loaded.

In the self-test position of the switch 17, the circuitry will simulatea NO-GO condition whereby the indicator 19 will reflect the white sideof the ball indicating that the test circuitry and power supply isworking satisfactory. If the test circuitry is faulty or the powersupply is low, however, the indicator 19 (in self-test) will reflect aG0 condition (the black side of the ball).

When the switch 17 is in the off position, the test circuitry isdisconnected from the batteries B1 and B2 which each are rated at 2.7volts. Since O2 is off during this time, a high voltage input may beapplied with no damage to the circuitry. Thus in the off position of theswitch 17, the contacts of the test probe may be applied to the firingcircuitry to test for the presence of a high voltage. Neon indicator 21will conduct, if approximately volts AC or volts DC is applied to theinput, to indicate a high voltage condition. The neon indicator 21 maybe energized regardless of the position of switch 17.

In the test position, the switch 17 connects the batteries B1 and B2 tothe test circuitry. When the switch 17 is moved to the test position,transistor Q11 is turned on which in turn turns on transistor 010 forabout 50 milliseconds. This connects one side of the indicator 19 to 2.7volts and resets the indicator 19 to the GO position. Since theindicator 19 is bistable it remains in the GO position until againreset.

Capacitor C5 is not charged when switch 17 initially is moved to thetest position. Capacitor C5 and resistor R23 have a time constantsufficient to allow Q11 to stay on for approximately 50 milliseconds.When transistor Q10 is on, it clamps the anode of programmableunijunction transistor Q9, through diode CR10, to approximately 2.1volts and holds it and Q5 and Q6 off. When Q5 and Q6 are off,transistors Q4, Q7, Q3, Q1, and Q2 are all off and the test circuit isdisconnected from the input. After the capacitor C5 charges to apositive enough level, Q11 turns off and Q10 turns off, allowing theemitters of the differential pair, transistors 05 and O6, to go toapproximately zero volts.

Resistors R11 and R12 form a voltage divider on the base of transistorQ5, which sets the threshold voltage of the differential pair toapproximately 0.5 volts. Since the bias on the base of Q5 is set whenthe switch 17 initially is moved to the test position, transistor Q5turns on after Q turns off. This turns on transistor Q4, which turns onthe connect transistor circuitry when an input is present. Thus thedifferential pair normally is latched (in the test position of switch17) in the condition with transistors Q4 and Q5 on and transistors Q6and Q7 off, since the base of transistor Q6 requires an input level ofO.5 volts from the filter to turn it on. In addition Q3 is on while Q8and Q10 are off.

If the input is essentially open circuit, i.e., mo emitter current intransistor Q2, then the transistor Q1 approaches turn-off. However whenan input is present, and Q4 is on, transistor Q1 provides base currentfor Q2, which turns on and connects the test circuit.

Whenever the input energy applied to the filter causes the filter outputto reach a level of 0.5 volts, transistor Q6 turns on, turning ontransistor Q7 and turning off transistors Q5 and Q4.

When transistor Q7 turns on, it provides base current through resistorR17 for transistor Q8, which turns on, and connects the indicator 19 to+2.7 volts, which sets it to the NO-GO position. At the same time,transistor Q7 connects resistor R18 to 2.7 volts and allows capacitor C4to charge through resistor R18, providing a time constant for theturn-on of the programmable unijunction transistor Q9. Approximately 40milliseconds after transistor Q7 turns on, Q9 then turns on and theanode of Q9 connects the emitters of the differentialpair transistors Q5and Q6 to 2.7 volts. This turns off Q5, Q6, Q4, Q1, Q2, Q3, and Q7 whichturns off Q8. In this condition, the test circuit is disconnected fromthe input. The circuit will remain in this condition until reset bymoving the switch 17 to the off position and then to the test position.

'Diode CR9 is provided as feedback to the base of Q6 such that wheneverQ7 turns on, it provides the base current path for Q6 instead of thefilter providing it. This insures a positive turn-on of Q6, and alsolowers the emitter of Q5 low enough to insure that Q5 turns off, thusproviding a latching feature in the differentialpair.

In the self-test position of the switch 17, the potentials of thebatteries B1 and B2 are again applied to the test circuitry but throughtransistors Q12 and Q13 which are turned on. However, in addition, thebattery B2 potential is applied to the emitter of the connect transistorQ2 through the diode CR5. In the self-test position, the reset sequenceis carried out whereby Q11 and Q10 are turned on to reset the indicator19. They are then turned off after about 50 milliseconds as indicatedpreviously. Whenever the reset sequence is completed, and the connecttransistor Q2 is turned on, the potentialprovided by battery B2 normallyis sufficient to simulate a NO-GO condition. Thus the output from thefilter 25 will reach a level of 0.5 volts whereby Q2 will be turned offand the indicator will be actuated to indicate a NO-GO condition whichindiates that the test circuitry is operating properly. If, however, thebattery potentials are low, or marginal, the circuit will not respond tothe simulated input and the NO-GO will not be registered and theindicator 19 will remain in its GO position, indicating that while inself-test, the test circuitry is not functioning properly.

Transistor Q3, resistor R6, and diodes CR6-CR8 form a unique turn-oncircuit for Q1 such that when the test set input is below approximately0.6 volts, the current through resistor R3 is small, limiting thebattery Bl current drain to approximately 8 milliamps and B2 currentdrain to 2.5 milliamps. This is accomplished when transistor Q4 turnson, turning the grounded base transistor Q3 on. For O3 to remain on, themaximum current allowable through resistor R6 is approximately 2milliamps. If the input is essentially an open circuit, ie, no emittercurrent in transistor Q2, then Q1 must approach turn-off since the onlycurrent path for the Q1 base and collector is ultimately through R6.However, when an input is present, and O4 is on, Q1 provides up to 32milliamps of base current for Q2, which turns on and connects the testcircuit. This amount of base current for O2 is required at highervoltage inputs because Q2 is required to conduct approximately 500milliamps of collector current; and to provide the constant inputimpedance feature. Diodes CR7 and CR8 are 300 volt diodes and establisha voltage level at which the transistor Q2 base must exceed to draw basecurrent. Diodes CR6-CR8 and transistor Q3 prevent transistor Q1 fromsaturation and allow it to provide current to transistor Q2 on a demandbasis.

When Q4 and Q3 are on, the voltage at the base of Q1 (determined by thevoltage drop across CR6) is fixed. When Q2 is fully turned on, becauseof the fixed base voltage of Q1, Q1 will draw a fixed amount of currentthrough R3 regardless of how hard Q2 turns on. This sets the constantbase current for Q2. When the input voltage to the test system is about0.6 volt, Q2 starts to turn on, however, it does not turn on fully untilthe input voltage is about 1.5 volts. At this point, Q2 is drawing thefull amount of base current and the voltage drop across the diode bridgeis about 0.7 volt while the base-emitter drop of O2 is about 0.7 volt.Since Q1 supplies current to Q2 when needed, it may be said to providecurrent to Q2 on a demand basis.

When the input voltage to the test system is above about 15 volts, thediode bridge drop and the baseemitter drop of Q2 become high enoughwhereby the input impedance does not remain constant.

In one embodiment, transistors Q2, Q1, and Q3 are identified as typesMJ423, MM4646, and MPS5172. Transistor Q2 is rated at about 300 volts aswell as transistor Q1. Diode CR6 is identified as lN4148, diodes CR7 andCR8 are identified as lN4003 respectively while diode CRll is identifiedas 7A14. Diodes CRl-CR4 are 300 volts germanium diodes, of the IN93type, and which have a low forward voltage drop. Resistor R3 is rated at76.8 ohms, resistor R4 at 1 kiliohms, and R5 and R6 at 680 ohms each.

The purpose of transistor Q14, diode CR1 1, and resistors R2, R22, R4,and R5 are'to insure that the circuitry operates properly at differenttemperatures.

Referring to FIG. 5, a front end switch 31 is disclosed for switchingout the diode bridge in order to make the system sensitive to inputvoltage levels below about 0.7 volts. The switch 31 comprises gangedswitch elements 33 and 35 which may be moved to contact terminals 23Cand 23D in order to carry out the tests described previously andemploying the function of the diode bridge. In order to test forvoltages at levels lower than 1.5 volts, the bridge is switched out bymoving the switch elements 33 and 35 to contact terminals 23E and 23Frespectively. This test applies the input directly to switch Q2 and isemployed after self-test and test is carried out as described previouslyand it has been determined that the stray energy level on the firingcircuit is low.

ln one embodiment the magnetic latching indicator 19 is of the type soldunder the trademark Minelco," a subsidiary of General Time of Holbrook,Mass, shown in their Bulletin B-llA entitled, Miniature Bite Indicator,"Model BHGZIT. The use of such magnetic latching indicators in the systemof the present invention has advantages in that they require a minimumamount of current for use. Thus a small current source may be employedin the system for long periods of time before replacement is required.

We claim:

1. A stray energy test system for measuring the stray energy on a firingcircuit employed on weapons release systems, comprising:

input means adapted to be coupled electrically to electrical contacts ofa system to be tested,

an electrical filter coupled to said input means for following apredetermined pulse width-voltage curve which is a function of the strayenergy which will cause the firing circuit to be actuated, said filterproducing a predetermined output when the input to said filterapproaches the voltage limit of said curve for a given time,

an indicator, and

threshold circuitry coupled to the output of said filter for actuatingsaid indicator when said predetermined output is produced.

2. The stray energy test system of claim 1 comprising:

circuitry including switch means coupled between said input means andsaid filter for passing to said filter, the energy applied to said inputmeans, and

said circuitry including said switch means having the characteristic ofmaintaining the current flow therethrough relatively constant above acertain voltage level to maintain constant the electrical inputimpedance to said filter as the input voltage to said switch meansvaries.

3. The stray energy test system of claim 2 comprising:

means coupled to said threshold circuitry and to said switch means forrendering said switch means nonconductive when said predetermined outputis applied to said threshold circuitry.

4. The stray energy test system of claim 3 comprising:

a source of electrical energy,

a control switch coupled to said source of electrical energy and adaptedto be moved to test or self-test terminal means to render said thresholdcircuitry in a state sufficient to sense for said predetermined output,

said self-test terminal means being coupled to the input of said switchmeans to enable said system to carry out self-testing operations,

said indicator being a magnetic latching type indicator having twostates and which must be actuated to position said indicator in one ofits states, and

said system including means for initially applying a voltage level tosaid indicator when said switch means is moved to either the test orself-test terminal means to initially set said indicator to one of itsstates.

5. The system of claim 4 comprising:

rectifier means coupled between said input means and said switch meansfor rectifying the input signal to be tested, and

a front end switch coupled between said input terminals and said switchmeans for bypassing said rectifier means and applying the input directlyto said switch means.

6. The stray energy test system of claim 3, wherein:

said filter comprises a two stage filter, one stage comprising aresistance-capacitance network providing a low frequency response filterand the other stage comprising a resistance-capacitance networkproviding a high frequency response filter.

7. The stray energy test system of claim 6, wherein: said switch meanscomprises a transitor having its emitter coupled to said input means andits collector coupled to said filter, and

means coupled to the base of said transitor for maintaining relativelyconstant the base current within a predetermined voltage range.

8. A stray energy test system for measuring the stray energy on a firingcircuit employed on weapons release systems, comprising:

input means adapted to be coupled electrically to electrical contacts ofa system to be tested,

an electrical filter coupled to said input means for following apredetermined pulse width-energy curve which is a function of the strayenergy which will cause the firing circuit to be actuated, said filterproducing a predetermined output when the input to said filterapproaches the energy limit of said curve for a given time,

an indicator,

switch means coupled between said input means and said filter forpassing to said filter the energy applied to said input means,

means for maintaining relatively constant the electrical input impedanceto said filter as the input to said switch means varies within a givenrange,

an indicator,

threshold circuitry coupled to the output of said filter for actuatingsaid indicator when said predetermined output is produced, and

means for rendering said switch means nonconductive when saidpredetermined output is applied to said threshold circuitry.

9. The stray energy test system of claim 8, comprising:

a source of electrical energy,

control switch means coupled to said source of electrical energy andadapted to be moved to test or self-test terminal means to render saidthreshold circuitry in a state sufficient to sense for saidpredetermined output,

said self'test terminal means being coupled to the input of said switchmeans to enable said system to carry out self-testing operations.

10. The stray energy test system of claim 8, wherein:

said indicator is a bi-stable latching type indicator having two statesand which must be actuated to position said indicator in one of itsstates,

said system including means for initially applying an input to saidindicator when said switch means is moved to either the test orself-test terminals to initially set said indicator to one of itsstates.

11. The stray energy test system of claim 8, wherein:

said filter comprises a two state filter,

will cause the firing circuit to be actuated, said filter producing apredetermined output when the input to said filter approaches the energylimit of said curve for a given time,

means for maintaining relatively constant the electrical input impedanceto said filter as the input to said test system varies within a givenrange,

an indicator, and

threshold circuitry coupled to the output of said filter for actuatingsaid indicator when said predetermined output is produced.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,778,709 Dated December 11, 1973 Inventor-(S) Robert A. Williams; DavidM. Holt It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

The title should be corrected to read as follows:

CURVE FOLLOWING STRAY ENERGY TEST SYSTEM Signed and sealed this 17th dayof September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

1. A stray energy test system for measuring the stray energy on a firingcircuit employed on weapons release systems, comprising: input meansadapted to be coupled electrically to electrical contacts of a system tobe tested, an electrical filter coupled to said input means forfollowing a predetermined pulse width-voltage curve which is a functionOf the stray energy which will cause the firing circuit to be actuated,said filter producing a predetermined output when the input to saidfilter approaches the voltage limit of said curve for a given time, anindicator, and threshold circuitry coupled to the output of said filterfor actuating said indicator when said predetermined output is produced.2. The stray energy test system of claim 1 comprising: circuitryincluding switch means coupled between said input means and said filterfor passing to said filter, the energy applied to said input means, andsaid circuitry including said switch means having the characteristic ofmaintaining the current flow therethrough relatively constant above acertain voltage level to maintain constant the electrical inputimpedance to said filter as the input voltage to said switch meansvaries.
 3. The stray energy test system of claim 2 comprising: meanscoupled to said threshold circuitry and to said switch means forrendering said switch means nonconductive when said predetermined outputis applied to said threshold circuitry.
 4. The stray energy test systemof claim 3 comprising: a source of electrical energy, a control switchcoupled to said source of electrical energy and adapted to be moved totest or self-test terminal means to render said threshold circuitry in astate sufficient to sense for said predetermined output, said self-testterminal means being coupled to the input of said switch means to enablesaid system to carry out self-testing operations, said indicator being amagnetic latching type indicator having two states and which must beactuated to position said indicator in one of its states, and saidsystem including means for initially applying a voltage level to saidindicator when said switch means is moved to either the test orself-test terminal means to initially set said indicator to one of itsstates.
 5. The system of claim 4 comprising: rectifier means coupledbetween said input means and said switch means for rectifying the inputsignal to be tested, and a front end switch coupled between said inputterminals and said switch means for bypassing said rectifier means andapplying the input directly to said switch means.
 6. The stray energytest system of claim 3, wherein: said filter comprises a two stagefilter, one stage comprising a resistance-capacitance network providinga low frequency response filter and the other stage comprising aresistance-capacitance network providing a high frequency responsefilter.
 7. The stray energy test system of claim 6, wherein: said switchmeans comprises a transitor having its emitter coupled to said inputmeans and its collector coupled to said filter, and means coupled to thebase of said transitor for maintaining relatively constant the basecurrent within a predetermined voltage range.
 8. A stray energy testsystem for measuring the stray energy on a firing circuit employed onweapons release systems, comprising: input means adapted to be coupledelectrically to electrical contacts of a system to be tested, anelectrical filter coupled to said input means for following apredetermined pulse width-energy curve which is a function of the strayenergy which will cause the firing circuit to be actuated, said filterproducing a predetermined output when the input to said filterapproaches the energy limit of said curve for a given time, anindicator, switch means coupled between said input means and said filterfor passing to said filter the energy applied to said input means, meansfor maintaining relatively constant the electrical input impedance tosaid filter as the input to said switch means varies within a givenrange, an indicator, threshold circuitry coupled to the output of saidfilter for actuating said indicator when said predetermined output isproduced, and means for rendering said switch means nonconductive whensaid predetermined output is applied to said threshold circuitry.
 9. Thestray energy test system of claim 8, comprising: a source of electricalenergy, control switch means coupled to said source of electrical energyand adapted to be moved to test or self-test terminal means to rendersaid threshold circuitry in a state sufficient to sense for saidpredetermined output, said self-test terminal means being coupled to theinput of said switch means to enable said system to carry outself-testing operations.
 10. The stray energy test system of claim 8,wherein: said indicator is a bi-stable latching type indicator havingtwo states and which must be actuated to position said indicator in oneof its states, said system including means for initially applying aninput to said indicator when said switch means is moved to either thetest or self-test terminals to initially set said indicator to one ofits states.
 11. The stray energy test system of claim 8, wherein: saidfilter comprises a two state filter, one stage comprising aresistance-capacitance network providing a low frequency responsefilter, the other stage comprising a resistance-capacitance networkproviding a low frequency response filter.
 12. A stray energy testsystem for measuring the stray energy on a firing circuit employed onweapons release systems, comprising: input means adapted to be coupledelectrically to electrical contacts of a system to be tested, anelectrical filter coupled to said input means for following apredetermined pulse width-energy curve which is a function of the strayenergy which will cause the firing circuit to be actuated, said filterproducing a predetermined output when the input to said filterapproaches the energy limit of said curve for a given time, means formaintaining relatively constant the electrical input impedance to saidfilter as the input to said test system varies within a given range, anindicator, and threshold circuitry coupled to the output of said filterfor actuating said indicator when said predetermined output is produced.